WO2019110103A1

WO2019110103A1 - Limit level sensor and method for operating same

Info

Publication number: WO2019110103A1
Application number: PCT/EP2017/081790
Authority: WO
Inventors: Levin Dieterle; Roland Baur
Original assignee: Vega Grieshaber Kg
Priority date: 2017-12-07
Filing date: 2017-12-07
Publication date: 2019-06-13
Also published as: DE112017008185A5

Abstract

The invention relates to a limit level sensor (1) having a microwave emitter (10) and a microwave receiver (11), a dielectric conductor (3) being arranged between the microwave emitter (10) and the microwave receiver (11).

Description

Point level sensor and method for its operation

The present invention relates to a point level sensor having the features of patent claim 1 and a method for level detection with the features of claim 9.

Point level sensors are basically known from the state of the art, for example for measuring limit or fill levels. Typical applications for detecting a predefined level are process vessels, such as process tanks, storage tanks, silos or pipelines in the process industry. Impedance sensors are often referred to as so-called.

Limit switch, i. to determine whether a filling medium exceeds or falls below a certain filling level, the so-called limit level, in different liquids, as well as

granulated and powdered bulk materials used.

There are various types of limit switches known, which are selected depending on the application, process conditions and characteristics of the filling medium. In addition to so-called impedance sensors come sensors that after the TDR (Time Domain

Reflectomety) principle, or vibration level sensors or capacitive sensors are used. A switching command of the limit switch can, for example, start or stop filling devices or emptying devices in order to correspondingly avoid overflowing or emptying of the respective process container.

It is the object of the present invention to propose an alternative alternative level sensor for liquids. An inventive level sensor has a Mikrowel lensender and a microwave receiver, wherein between the microwave transmitter and the microwave receiver

dielectric conductor is arranged.

Under microwaves in the present application elekt romagnetische waves of a frequency of 30 GHz to 100 GHz.

An inventive limit level sensor thus has no moving parts and altogether only a very few parts. In particular, the number of parts that come in contact with a filling medium in contact is reduced to a minimum.

The present level sensor is the recognition zugrun de that electromagnetic microwaves are conducted in a be in air-sensitive dielectric conductor due to total reflection at the interface between the dielectric and the air in the dielectric conductor. The total reflection takes place on account of the permittivity jump between the dielectric and the air occurring at the interface. A signal emitted by the microwave transmitter remains so within half of the dielectric conductor and emerges only at the end again.

If the dielectric conductor is in a medium of high permittivity, which applies to a multiplicity of liquids, the microwaves emerge to a greater extent from the dielectric. The signal strength of a signal arriving at the microwave receiver is thereby reduced. This reduction of the signal strength can be detected and concluded based on the presence of a medium and thus the reaching of the limit level. In the present measurement principle so that only a sufficient part of the dielectric conductor must come into contact with the measuring medium, so that a sufficient reduction of the Emp catch signal compared to the transmission signal is achieved. Other components in medium contact are not necessary.

The above effect that the microwaves emanating from the lektrischen conductor is achieved in that the dielectric conductor has a bend. The conduction of an electromagnetic wave in a dielectric conductor is based on the different permittivity of the conducting medium and the surrounding medium. This sets a maximum possible angle for a reflection. Once this angle is exceeded, the shaft exits. The bend is dimensioned so that in the surrounding medium air still very few waves emerge. As soon as another medium comes into contact with a higher permittivity at the bend, the maximum possible angle changes for a nearly lossless waveguide. A larger portion of the electromagnetic wave occurs.

In the present application, a bend should not only be understood to mean a continuous change in direction of the dielectric conductor, but any directional change which changes the angle of incidence of the coupled-in electromagnetic radiation relative to the interface or the respective surface normal.

At a bend, the microwaves impinge on the interface between the dielectric conductor and the surroundings at a smaller angle relative to the interface normal, so that a larger proportion is transmitted when a medium is present, ie, transferred from the dielectric conductor into the medium. occurs. Accordingly, a drop in the signal strength at the output of the dielectric conductor is greater, so that a simpler De detection of the waste is possible.

In an advantageous embodiment, an angle between tween a coupling axis and a Auskoppelachse is at least 50-60 °, preferably at least 90 °, more preferably 180 °.

Under coupling axis to be understood in the present application, a longitudinal axis of the dielectric conductor in the region of a coupling portion of the dielectric conductor who the. Accordingly, the coupling-out axis should correspond to the longitudinal axis of the dielectric conductor in the region of a coupling-out section.

In a preferred embodiment, the dielectric conductor is formed substantially U-shaped bent. In this case, the coupling-in axis and the coupling-out axis are parallel to one another. This is also the case with a 180 ° bend.

A U-shaped configuration of the bend thus has the part before that the microwave transmitter and the microwave receiver can be arranged side by side. In particular, it is in this way very easy to arrange Mirowellen transmitter and microwave receiver on a common electronic board. The two can be connected in this way also particularly simple with other components eg. For signal generation and evaluation.

Depending on the material used and prevailing ambient conditions, it may be useful if a support device at least partially supports the dielectric conductor. Such a support device can in particular be adapted to a contour and shape of the dielectric conductor and preferably support this on the inside.

On the inside should mean in this context, in particular the nenradius in a possibly existing bend. In this way it is ensured that the influence of the support device is minimized. The support device may for example be made of a metal, which includes the lektrischen the conductor at an inlet and outlet from the process space and otherwise supported on the inside.

Other materials may be any materials with a significantly higher permittivity than the dielectric conductor, which is adapted in its properties to the conditions of use. For example, plastics, glass or ceramics are conceivable

The dielectric conductor may, for example, be made of a plastic, in particular polytetrafluoroethylene (PTFE), polyethylene (PE) or polyetheretherketone (PEEK), a ceramic.

Basically, all plastics that have a relatively low permittivity and can withstand the process conditions of measuring the medium are suitable. The higher the permittivity of the electrical conductor, the more the number of measurable media is limited due to the necessary difference in permittivity.

Plastics have the advantage that they can be produced by injection molding or extrusion in almost any shape. For putting in, for example, polytetrafluoroethylene is highly chemically resis tent, high temperature resistant and has 2.1 for the present application optimally suitable relative Dielektrizi- tätszahl on. Further, PTFE is relatively insensitive to buildup.

Suitable ceramics can, for example, be brought into a suitable shape by sintering. These have the advantage of a higher stability against abrasive media and against some solvents and are compared to plastics significantly temperature-stable.

A broad applicability of the level sensor can be achieved if the dielectric conductor has a relative permittivity of less than 10, in particular less than 5, preferably 2.1. With a suitable relative permittivity on the one hand sufficient total reflection is achieved in the situation without medium contact, since the jump at the boundary of the dielectric conductor is sufficiently high, on the other hand, the transition of a sufficient amount of electromagnetic waves is ensured in the medium, as liquids typi cally a relative Have permittivity above these values.

An inventive method for level detection with a point level sensor according to the above description comprises the following steps:

- Send a microwave signal in the dielectric conductor

as a transmission signal

- Receiving a received signal

- Compare the received signal strength with the transmit signal strength and

- Outputting a level signal based on the comparison. It can be concluded based on a comparison of the transmission signal and the Emp catch signal on whether the dielectric conductor is surrounded with a, preferably liquid, filling medium or not. This can be achieved in particular by comparing the signal powers of the transmission signal and the received signal.

This is due to the above-described effect that electro magnetic microwaves in an air in the lektrischen conductor due to a total reflection at the boundary surface between the dielectric and the air in which the lektrischen conductor are passed. Total reflection takes place on account of the permittivity jump between dielectric and air occurring at the interface. A signal emitted by the micro wave transmitter thus remains within the dielectric conductor and only emerges at its end.

If the dielectric conductor is in a medium of high permittivity, which applies to a multiplicity of liquids, the microwaves emerge to a greater extent from the dielectric. The signal strength of a signal arriving at the microwave receiver is thereby reduced. This reduction of the signal strength can be detected and concluded based on the presence of a medium and thus the reaching of the limit level.

Particularly easy, a threshold signal can be achieved when the step of comparing a comparison of a Sig nalleistung of the transmission signal with a signal power of Emp fangssignals comprises and an empty signal is output, as long as the power of the received signal more than, for example, 70% of the amplitude of the transmission signal is and a full signal is output when the receiving power is, for example, 70% or less of the power of the transmission signal. The dif ference between transmitting and receiving power is u. A. depending on the frequency used, the length and the material of the dielectric conductor, the diameter of the dielectric conductor and can therefore be given only as an example. In a simulation with PEEK as the material for the dielectric conductor and when using a frequency of 75 GHz, the reception power in air is about 10% of the transmitter power, with medium contact still in the order of 0.01-0.1%.

The present invention will be explained below in detail with reference to the accompanying figures.

Show it:

FIG. 1 is a schematic view of a microwave

Point level sensor according to the present application,

FIG. 2 shows the field distribution in the sensor according to FIG. 1 in FIG

air and

3 shows the field distribution in the sensor according to Figure 1, when it is partially covered with water.

FIG. 1 shows a schematic representation of a microwave level sensor 1 according to the present application.

The microwave level sensor 1 is essentially formed from egg nem bent dielectric conductor 3 with a Eingangsab section 31, an output section 32 and an interposed bend 33 of the dielectric conductor 3. On the input side, the dielectric conductor 3 is connected to a micro-wave transmitter 10, which couples electromagnetic microwaves, that is, electromagnetic radiation in the gigahertz range in the dielectric conductor 3 in the direction of a coupling axis E. The coupling axis E corresponds essentially to a longitudinal axis of the input section 31 of the dielectric conductor 3 which extends in this area substantially longitudinally and is straight. The dielectric conductor 3 has in the present embodiment, a circular cross-section, but may also be formed, for example. Oval or shaped differently.

Analogous to the input-side structure of the dielectric conductor 3 on the output side with a microwave receiver 11 a related party. The microwave receiver 11 is arranged substantially in extension of a coupling-out axis A, which essentially corresponds to a longitudinal axis of the dielectric conductor 3 in the region of the output section 32. In this way it can be detected that electromagnetic radiation leaves the dielectric conductor 3. The electromagnetic

Radiation which has left the dielectric conductor 3 no longer arrives at the microwave receiver and can therefore no longer be detected there. One of the Microwave lenempfänger and the microwave transmitter connected Auswer teelektronik 12 detects a difference between transmit and Emp catch power and can derive therefrom the level information.

The dielectric conductor 3 is formed in the present Ausführungsbei game of polytetrafluoroethylene (PTFE). This material has a relative permittivity ∈ _r of 2.1, so that coupled electromagnetic radiation when the dielectric conductor 3 is in air is due to total internal reflection. is conducted within the dielectric conductor 3. This To talreflexion also takes place in the region of the bend 33. Be is the dielectric conductor 3 so in air, the microwave receiver 11 can detect a certain proportion of the electro-magnetic radiation, which was coupled by the microwave transmitter 10 in the dielectric conductor 3.

In the present embodiment, PEEK was used as the material for the dielectric guide 3 and a signal frequency of 75 GHz. In air, the received power is still about 10% of the transmission power.

In order to ensure sufficient stability of the present arrangement, a support device 5 (number missing in the sketch) is arranged within the dielectric conductor 3, that is to say in particular between the input section 31 and the output section 32 and in the region of the bend 33.

The support device 5 is designed so that it is adapted We sentlichen the shape and contour of the dielectric conductor 3 and this on the mutually facing Innenflä surfaces of the contour of the dielectric conductor 3 is supported.

The support device 5 is made in the present embodiment of a metallic material, since this is not a dielectric conductor. At the beginning of the input section 31 and at the output of the output section 32, the Stützvor device 5 includes the dielectric conductor 3 with support rings 51 completely, so that it is particularly protected in this area against a Abkni bridges. In the further course of the input portion 31 and the output portion 32 and in Be rich the bend 33, a support filling 52 is arranged, which receives and supports only an inner portion of the contour of the dielectric rule's conductor 3. The support filling 52 also prevents unwanted deposits in the inner area of the bend. In particular, in the area of the bend 33, it is crucial that an outer radius of the bend 33 is freely accessible to the filling medium, so that the effect of vorlie lowing measuring principle can occur.

If the dielectric conductor 3 of the level sensor 1 according to the present application at least partially, in particular in the region of the bend 33 in a liquid Füllme medium whose limit level is to be monitored, it is surrounded in this area by a medium which a Permitti- Although in this constellation, the coupled electromagnetic waves while well in the region of the Eingangsab 31 are still performed well within the dielectric conductor 3, in the region of the bend 33 but there is no total re flexion more , so that a large part of the coupled electromagnetic radiation in the region of the bend 33 emerges from the dielectric conductor 3. The detectable at Mikrowellenemp catcher 11 electromagnetic radiation decreases so significantly, so it can be concluded that the presence of a medium.

Both the microwave transmitter 10 and the Mikrowellenemp catcher 11 can be coupled in the present embodiment, in each case via a waveguide, which is not shown here, to the dielectric conductor 3. Typically, the dielectric conductor 3 is guided into the waveguide and sharpened in the region of the waveguide so that the electromagnetic radiation generated by the microwave transmitter 10 is transmitted into the dielectric conductor 3 in the region of the waveguide or correspondingly from the dielectric Leader end exits and can be detected by the microwave receiver 11.

FIG. 2 shows a field distribution within the dielectric conductor 3 and in its surroundings when it is in air. As can be seen from FIG. 2, a very large part of the electromagnetic field coupled on the input side is guided by total reflection in the dielectric conductor so that it can be detected on the output side. The Totalrefle xion also takes place in the region of the bend 33, wherein the electromagnetic radiation is reflected in particular in this area at the jump in relative permittivity of the material of the lektrischen conductor 3 to the surrounding air.

In Figure 3, the dielectric conductor of Figure 2 Darge presents, wherein in the region of the bend 33, a filling medium, in front of lying water is arranged. As is clearly known from FIG. 3, in the region of the bend 33, a large part of the electromagnetic radiation coupled in on the input side emerges from the dielectric conductor 3, so that only a fraction of the electromagnetic radiation can be detected on the output side. By comparing a power of the input signal with a power of the output signal can thus be closed in a simple manner to the presence of a Füllmedi order and give a corresponding level signal out. LIST OF REFERENCE NUMBERS

I point level sensor

3 dielectric conductor

5 supporting _V orrichtung

10 microwave transmitters

II microwave receiver

12 transmitter

31 entry section

32 output section

51 support rings

52 supporting filling

E coupling axis

A coupling-out axis

Claims

claims

1. Point level sensor (1) with

a microwave transmitter (10) and a Mikrowellenempfän ger (11), wherein between the microwave transmitter (10) and the microwave receiver (11) a dielectric conductor (3) is arranged.

2. point level sensor (1) according to claim 1,

d a d u r c h e c e n c i n e s that

the dielectric conductor (3) has a bend (33).

3. point level sensor (1) according to claim 2,

d a d u r c h e c e n c i n e s that

an angle between a Einkoppelachse (E) and a Auskoppelachse (A) at least 45 °, preferably wenigs least 90 °, more preferably 180 °.

4. point level sensor (1) according to claim 2,

d a d u r c h e c e n c i n e s that

the dielectric conductor (3) is formed in a substantially U-shaped manner.

5. point level sensor (1) according to one of the preceding claims,

d a d u r c h e c e n c i n e s that

a support device (5) at least partially supports the dielectric conductor (3).

6. point level sensor (1) according to claim 5,

d a d u r c h e c e n c i n e s that

the supporting device (5) to a contour and shape of the Lektrischen conductor (3) is adapted and this inside supported.

7. point level sensor (1) according to one of the preceding claims,

d a d u r c h e c e n c i n e s that

the dielectric conductor (3) is made of a plastic, in particular special polytetrafluoroethylene, polyethylene or polyether retherketone, a ceramic.

8. Point level sensor (1) according to one of the preceding claims,

d a d u r c h e c e n c i n e s that

the dielectric conductor (3) has a relative dielectric constant of less than 10, in particular less than 5, preferably 2, 1.

9. Level detection method with a limit

Stand sensor (1) according to one of the preceding claims, comprising the following steps:

- Send a microwave signal in the dielectric's conductor as a transmission signal

- Receiving a received signal

- Comparing the received signal with the transmission signal and

- Outputting a level signal based on this comparison.

10. The method according to claim 9,

d a d u r c h e c e n c i n e s that

the step of comparing comprises comparing a signal power of the transmission signal with a signal power of the reception signal and outputting an empty signal as long as the power of the reception signal exceeds the defined as switching threshold minimum share of

Power of the transmission signal and a full signal is output when the received power defined as the switching threshold minimum power

or less.